In producing magnetic recording media, there is a recurring need to transport large quantities of recording tape from the point of tape manufacture to other locations for final loading into cassettes, cartridges, or other carriers. It is common to transport the tape in the form of relatively large rolls, called "pancakes." A pancake of 1.27 cm (0.5 in) wide tape is typically wound on a hollow annular core having an outer diameter of 11.4 cm (4.5 in), and a width of 1.8 cm (0.7 in), slightly larger than the width of the tape. The outer diameter of the pancakes is typically about 35.6-40.7 cm (14-16 in). Shipping these tape pancakes over long distances under conditions of mechanical shock and vibration requires that they be well supported.
One primary form of damage to pancakes is axial shifting of the layers of tape relative to the pancake such that the pancake is no longer flat. This shifting, called "core drop" or "hub drop," is measured by laying the pancake on a flat surface and measuring the height of the tape portion of the pancake at the inner and outer radii. Measurements are made both before and after subjecting the pancake to shock or vibration. Core drop during shipping is typically caused by a stack of pancakes being dropped on a hard floor or being transported over rough or bumpy surfaces. Other problems and damage caused with known pancake containers include the offsetting of a portion of the pancake, called "upset," rotation of the core relative to the pancake, and transfer of cushion adhesive to the tape.
While effective protection of the tape in the pancake stacks is essential, the magnetic tape market is very price-competitive. Therefore, protective packaging must be low cost, both in the packaging material itself, and in the labor required to apply and remove the packaging. It is also desirable to minimize the amount of packaging waste material which must be discarded.
Known methods of protecting pancakes during shipping generally involve sliding several pancakes over a shaft or hollow tube, placing resilient spacers between each pancake, and disposing a solid end plate on the top and bottom of the stack. The stack can be held together by shrink wrap film, as disclosed in U.S. Pat. No. 4,955,471. However, the application and removal of shrink wrap film is very labor-intensive. Removal can involve cutting or other operations which can damage the pancake and generate waste which can contaminate the tape. Also, shrink wrap is not reusable, thereby increasing costs.
The shrink wrap removal problem is addressed in U.S. Pat. No. 4,708,246, assigned to Minnesota Mining and Manufacturing Company. This patent discloses grooves in the outer surface of the package to allow a knife to cut the shrink wrap without contacting the inner packaging material. This is accomplished by running the knife along the groove, without penetrating beyond the depth of the groove as the shrink wrap is cut.
U.S Pat. No. 4,883,178 eliminates shrink wrap. This patent discloses holding the stack together with a threaded member running coaxially along the center of the stack, and a nut which tightens on an endplate. The compression is created by the threaded member being disposed within the pancake cores. This method is less labor intensive than shrink wrap, but it does not enclose the stack, so that additional wrapping may still be required.
Whenever axial compression is used to hold the pancakes together, the compression itself may damage the pancakes or their cores. U.S. Pat. No. 4,708,246 discloses spacers and other packaging features which improve compression control. However, sometimes spacers move during shipping and can generate debris. Also, some spacer materials can create static which attracts debris to the pancakes.
Radially expanding mandrels are also known. U.S. Pat. No. 4,124,173 discloses an inflatable tube inside of an expandable mandrel. Cam mechanisms which press cylinder segments outwardly when a central shaft rotates relative to the outer segments are also known. U.S. Pat. No. 4,516,786 discloses a rotatable core chuck and U.S. Pat. No. 4,730,779 discloses an expanding assembly for a web-coiling core. These cores are used in rotating apparatus and must be heavy and complex to accommodate the dynamics of rotating environments.
In the majority of cases, the pancake is placed on an unwind apparatus to feed the tape into a cassette or cartridge loading machine. The pancake is loaded onto the machine with the core axis horizontal. Since a typical pancake can weigh over 7.8N (4 lb), the effort required to remove pancakes from their package and place them on the unwind apparatus is significant. Additionally, most known pancake packaging stacks the pancakes vertically. This requires the extra step of either tipping the entire stack or individual pancakes to a position with a horizontal axis before loading the pancakes onto the loading machine. Due to the weight of the pancakes and the repetitive nature of this task in production, worker fatigue and injury can be significant problems. It is desirable that the packaging be ergonomically designed to reduce the effort required to load the pancakes onto the loading machine without risking tape damage, or injury to the workers.